The present invention relates to an improvement for the insulation structure of a rotary-type heat exchanger, and more particularly for one suitable for rotary-type heat exchangers for high temperature.
Gas of temperatures as high as several hundreds to over 1,000.degree. C. is exhausted from boilers, engines, incinerators, furnaces and various other devices. As the save-energy campaign has actively been promoted in recent years, those exhaust gas has attracted much attention as a potential source of energy. However, as those exhaust gas is often contaminated, it is necessary to heat-exchange it with clean gas such as the outer air so that the heated new gas is supplied to a boiler for combustion.
When a rotary-type heat exchanger is used for such a heat exchange process, the gas used is of a considerably high temperature, and therefore it should have a heat-resistant structure. This often causes following problems:
(1) When the gas used is 800.degree. C. or higher, a casing which houses a rotor and which is generally made of stainless steel can not endure the high temperature. The casing must therefore be made of Mn steel or other heat-resistant special metals, brick of ceramics or must be provided with a special cooling device such as water-cooled fins. But those heat-resistant or insulated casings are expensive in material, manufacturing and installation costs, consequently pushing up the price of a rotary-type heat exchanger. This will thwart the save-energy campaign.
(2) The bearings which support the rotor, a driving mechanism therefor and sealing means for the gas must be made of heat-resistant materials. This further pushes up the cost.
The rotor made of ceramics and therefor having a good heat resistance can withstand temperatures of 1,000.degree. C. or more is available.
As described in the foregoing, in prior art rotary-type heat exchangers for high temperature, various special parts must be used in order to give heat resistance to various locations other than the rotor. This unavoidably makes the cost quite expensive without leaving much economical gain from the recycling of the heat in the exhaust gas.
The present invention aims to obviate above mentioned defects encountered in prior art and to provide a rotary-type heat exchanger which is low in cost and excellent in heat resistance. Such object can be attained by limiting the area which is subjected to high temperatures. In other words, as the rotor in a rotary-type heat exchanger has gas passages in the direction of the shaft alone and has little heat transmission in the radial direction, the gas of high temperature to be used in the heat exchanger passes only through the rotor, and more particularly the areas of the rotor other than those in the vicinity of its shaft and outer periphery while the new low temperature gas with which the heat exchange is to be conducted is passed through all the areas of the rotor other than those where the high temperature gas is passed as well as through the voids between the rotor and the casing. This cools the casing, the rotor bearings and the driving mechanism with the gas of lower temperature and blocks them from the gas of high temperature without necessitating special parts made for special heat resistance. In short, special heat-resistance has to be provided only to the inner wall of the inlet for the hot gas, the sealing member for preventing leak of the gas and the inner wall of the outlet for the new hot gas which has been heat-exchanged and heated to a high temperature. The cost of component parts is thus remarkably reduced, the insulation work is simplified, and an inexpensive rotary-type heat exchanger for high temperature is attained.